This application includes a microfiche appendix including one microfiche and 14 frames.
The present invention relates to an ultrasonic system for detecting intrusion of objects or persons into a monitored area.
Ultrasonic intrusion detection systems are known wherein reflected wave patterns are compared to reference patterns such as described in U.S. Pat. No. 4,499,564, issued on 12 Feb. 1985 to Sirai. In this system, the reference pattern is based upon the statistical mean values of a plurality of reflected waves. Then reflected wave patterns are statistically compared to the reference pattern and an alarm is energized when a sampling point of the reflected wave differs from a corresponding point of the reference pattern by more than a standard deviation.
A microprocessor-based system is described in U.S. Pat. No. 4,800,540, issued 24 Jan. 1989 to Annala. In this system, 100 bursts are processed and a reference table is generated which includes echo or no-echo flag values only for sample time points which consistently yield indications of echoes or non-echoes, respectively. Then, in a detection mode, portions of the reference table which include transitions in adjacent locations and the corresponding sampled signal locations are ignored.
Such systems are complex and are intended to filter out background noise and to reduce erroneous alarm indications. However, when such a system is to be adapted for use on a vehicle or on a piece of heavy machinery, then safety becomes of primary importance. For purposes of safety, it is preferable to accept some erroneous indications in the interest of insuring that legitimate intrusions produce an alarm signal. Accordingly, a relatively simple intrusion detection system which enhances safety is desired.